Hardness testing devices of the various types heretofore known have primarily been based on the use of a hardened probe or indenter for penetrating the surface of a test piece under a prescribed load and measuring the depth of penetration as a function of the hardness of the surface stratum of such test piece. A variety of designs of probes or indenters have heretofore been used including ball-shaped indenters composed of hard material, such as metal carbide materials, as well as pyramidal-shaped indenters composed of industrial diamonds. Material hardness testers of the foregoing type employ a constant pressure and measure the depth of penetration, while others measure the pressure required to effect a penetration of the indenter into the surface stratum of a workpiece to a pre-established depth. In either case, the penetrating force required and the depth of penetration of the indentor are directed proportional to the hardness of the test piece.
While hardness testers of the types heretofore known have been satisfactory to provide accurate measurements of the hardness of workpieces and test pieces as a laboratory test device, their adaptation as a high-speed, automatic quality control device on a commercial production scale has not been effective due to the general tedious and time-consuming steps required in effecting a measurement of the hardness of the workpiece, as well as the sophistication of controls required and the costs associated in achieving fast and accurate readings. Problems have also been encountered with prior art testing devices in that the hardness masurement is taken between the indenter or penetrating probe and a supporting anvil on which the test piece is positioned such that any foreign matter between the anvil and the workpiece results in inaccuracies in the hardness reading of such devices.
The present invention overcomes many of the problems and disadvantages associated with prior art type materials hardness testers, which is of durable construction, rapid and substantially maintenance-free operation, which is of versatile use and can readily be adapted to different test conditions and workpieces, which can readily be adapted for automatic operation for measuring successive workpieces produced at commercial production rates, which can readily be adapted to produce an audible and/or visual signal identifying and/or rejecting test pieces which do not fall within a prescribed range of acceptable hardnesses and which is of economical cost and operation.